Data has been obtained from academic publications (from 2002 onwards); if the mean value was not available, a range is given. "0" indicates "zero" òr "below detection limits". Pollution levels may be season-dependent in some cases, which has been ignored in this graph. Please note that locations are not exact. This figure has been compiled and will be updated regularly with the greatest possible care, but no rights may be derived from its contents. This graph was made with Plotly for R.